Powered fuel combustion burner with nozzle flow guide

ABSTRACT

A combustion burner includes a mixture nozzle, a gas supply nozzle, and a flow guide. The mixture nozzle extends toward an interior of a furnace, and defines a mixture passage through which a mixture containing powdered solid fuel and gas for transferring the solid fuel flows. A distal end portion of the mixture nozzle is flared so that a flow passage area of the mixture passage increases progressively in a direction of flow of the mixture. The gas supply nozzle radially surrounds the mixture nozzle to define between the gas supply nozzle and the mixture nozzle a gas passage through which a combustion oxygen-containing gas flows toward the furnace. The flow guide is provided within the mixture nozzle at a position upstream of the flared portion of the mixture nozzle with respect to a flow of the mixture so as to make the mixture flow straight along an inner peripheral surface of the flared portion of the mixture nozzle.

TECHNICAL FIELD

This invention relates to a combustion burner.

BACKGROUND OF THE INVENTION

A burner of this type comprises a mixture nozzle, and a gas supplynozzle surrounding this mixture nozzle.

In a pulverized coal burner disclosed in JP-A-63-87508, an impeller forswirling an air-fuel mixture is provided within a mixture nozzle. Theswirled mixture from an outlet of the mixture nozzle is rapidly diffusedwithin a furnace, and is mixed with secondary air and tertiary air,supplied from a gas supply nozzle, in the vicinity of the outlet of themixture nozzle. Therefore, a reduction area is not sufficiently formed,and a flame does not spread in the furnace. As a result, a part of finepulverized coal remains unburned, and the production of NOx can not besuppressed.

In a pulverized coal burner disclosed in JP-A-60-200008, a throatportion is provided within a mixture nozzle, and an outlet of themixture nozzle is flared. In this burner, as in the above-mentionedburner, an air-fuel mixture from an outlet of the mixture nozzle israpidly diffused within a furnace, and is mixed with secondary air andtertiary air, supplied from a gas supply nozzle, in the vicinity of theoutlet of the mixture nozzle. As a result, a part of fine pulverizedcoal remains unburned, and the production of NOx can not be suppressed.

BRIEF SUMMARY OF THE INVENTION

It is an object of this invention to provide a combustion burner whichsolves these problems, and can achieve low-NOx combustion.

To this end, according to one aspect of the present invention, there isprovided a combustion burner comprising: a mixture nozzle which extendstoward an interior of a furnace, and defines a mixture passage throughwhich a mixture containing powdered solid fuel and gas for transferringthe solid fuel flows, and a distal end portion of which mixture nozzleis flared so that a flow passage area of the mixture passage increasesprogressively in a direction of flow of the mixture; a gas supply nozzleradially surrounding the mixture nozzle and defining between the gassupply nozzle and the mixture nozzle a gas passage through whichcombustion oxygen-containing gas flows towards the furnace; and guidemeans provided within the mixture nozzle at a position upstream of theflared portion of the mixture nozzle with respect to a flow of themixture so as to make the mixture flow straightly along an innerperipheral surface of the flared portion of the mixture nozzle.

According to another aspect of the present invention, there is provideda combustion burner comprising: a mixture nozzle extending towards aninterior of a furnace, and defining a mixture passage through which amixture containing powdered solid fuel and gas for transferring thesolid fuel flows, and a distal end portion of which mixture nozzle isflared so that a flow passage area of the mixture passage increasesprogressively in a direction of flow of the mixture; a gas supply nozzleradially surrounding the mixture nozzle, and defining between the gassupply nozzle and the mixture nozzle a gas passage, through whichcombustion oxygen-containing gas flows towards the furnace, and a gasjet nozzle through which gas is injected radial inwardly towards themixture flowed into the furnace from the distal end of the mixturenozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a burner of thepresent invention;

FIG. 2 is a cross-sectional view of a furnace of a boiler using theburners of FIG. 1, showing a condition of a flame in the furnace;

FIG. 3 is a cross-sectional view taken along the line III--III of FIG.2;

FIG. 4 is a cross-sectional view showing the condition of the flame inthe furnace;

FIG. 5 is a cross-sectional view showing a flow of a mixture and a flowof combustion air in the burner;

FIG. 6 is a cross-sectional view showing a condition of a flame in afurnace using a conventional burner;

FIG. 7 is a cross-sectional view of the furnace of a boiler using theconventional burners, showing the condition of the flame in the furnace;

FIG. 8 is a cross-sectional view taken along the line VIII--VIII of FIG.7;

FIG. 9 is a cross-sectional view showing another embodiment of a burner;

FIG. 10 is a cross-sectional view taken along the line X--X of FIG. 9;

FIGS. 11 to 13 are cross-sectional views showing further embodiments ofburners, respectively;

FIG. 14 is a cross-sectional view showing a further embodiment of aburner;

FIG. 15 is a cross-sectional view taken along the line XV--XV of FIG.14;

FIGS. 15A to 15D are front-elevational views respectively showingmodified air injection nozzle constructions of a burner of FIG. 14;

FIG. 16 is a fragmentary, cross-sectional view showing a condition offlow of a mixture and a condition of flow of combustion gas in thevicinity of an outlet of the burner shown in FIG. 14;

FIG. 17 is a cross-sectional view taken along the line XVII--XVII ofFIG. 16;

FIG. 18 is a cross-sectional view showing another embodiment of aburner;

FIG. 19 is a cross-sectional view taken along the line XIX--XIX of FIG.18; and

FIG. 20 is a cross-sectional view showing a further embodiment of aburner.

DETAILED DESCRIPTION OF THE INVENTION

A combustion burner 1 according to one embodiment of the presentinvention shown in FIG. 1, which is used in a boiler, comprises amixture nozzle 10 through which a mixture 12 containing fine pulverizedcoal as solid fuel and primary air for transferring purposes flows. Inthis embodiment, as shown in FIGS. 2 and 3, twelve combustion burners 1are arranged in an opposed manner in a common horizontal plane at afurnace 3, and also the combustion burners are arranged in three stagesin a vertical direction. However, the number of the burners 1 as well asthe number of stage is not limited to this arrangement.

The mixture 12 is supplied via the nozzle 10 into the furnace 3 throughan opening 30 formed in the furnace 3. A gas supply nozzle 20 isprovided around the nozzle 10. A secondary air passage 21 is definedbetween the nozzle 10 and the nozzle 20, and a tertiary air passage 31is defined between the nozzle 20 and the opening 30 of the furnace 3. Aswirl-producing device 23 is provided in the secondary air passage 21 soas to swirl the secondary air 22 from a wind box 4. A swirl-producingdevice 33 is provided in the tertiary air passage 31 so as to swirl thetertiary air 32 from the wind box 4.

A ring-shaped flame stabilizer 13 is provided at a distal end of thenozzle 10, which has a peripheral edge portion of an L-shapedcross-section. A distal end portion 14 of the nozzle 10 is flared sothat its flow passage area increases progressively along the flow of themixture 12.

A guide 51 is disposed in the nozzle 10 so that the mixture 12 can flowradially outwardly along the flared distal end portion 14. The guide 51is provided at a distal end of an oil burner 52. The oil burner 52 isused when activating the boiler and in a low-load condition. In the casewhere no oil burner is needed, the guide 51 is placed by a suitablesupport.

The guide 51 has a first guide portion 511, a second guide portion 512and a third guide portion 513 along the flow of the mixture 12. Theoutside dimension of the first guide portion 511 increases progressivelyin the direction of flow of the mixture 12, and the outside dimension ofthe third guide portion 513 decreases progressively in the direction offlow of the mixture 12. Both are interconnected by the second guideportion 512 having a constant outside dimension. The guide 51 is locatedupstream side of the flared distal end portion 14 with respect to theflow of the mixture 12.

In the burner 1 of this construction, a flame 5 is spread outwardly asshown in FIG. 4. As a result, unavailable areas NA of the furnace arereduced as shown in FIGS. 2 and 3. Air supply ports 6 are provideddownstream of the burners 1, and additional air 62 is supplied into thefurnace 3 through these air supply ports. In reduction areas RAdelimited by the flames 5 from the most downstream burners 1 and theadditional air flows 62 from the air ports 6, the combustion gas staysfor a longer time period. Therefore, the NOx concentration in thecombustion gas is reduced, so that the combustion efficiency isenhanced. The unburned pulverized coal is completely burned by the air62 from the air ports 6.

The momentum of the pulverized coal is greater than that of the primaryair, and therefore the pulverized coal is condensed at a region close tothe peripheral wall of the flared distal end portion 14 of the nozzle10, as shown in FIG. 5. Therefore, the combustion efficiency in thevicinity of the outlet of the burner is enhanced, so that the flame 5 isthermally expanded to be more spread.

In this embodiment, the nozzle 20 is provided at a distal end thereofwith separation means in the form of a flared, annular deflection guidetube 24. Accordingly, the primary air 22 and the tertiary air 23, whichare swirled respectively by the swirl-producing devices, flow forwardlyand radially outwardly. As shown in the drawings, if the annulardeflection guide tube 24 is so designed that the angle θ₁ between theannular deflection guide tube 24 and the axis of the mixture nozzle 10is equal to or larger than the angle θ₂ between the flared distal endportion 14 and the axis of the mixture nozzle 10, the secondary air andthe tertiary air are more spread radially outwardly. As a result, anair-insufficient area, that is, a fuel-excessive area is formed in acentral portion of the flame, thereby enabling the low NOx combustion.

On the other hand, in a conventional burner shown in FIG. 6, a mixturenozzle 10 does not have the flared distal end portion 14, and the guide51 is not provided within the mixture nozzle. Therefore, a flame doesnot spread, but behaves as a free jet. As a result, as shown in FIGS. 7and 8, the area in a furnace 3 where flames are not present, that is,the unavailable area NA in the furnace become larger as compared withthe furnace of FIGS. 2 and 3. Further, the time period of stay of thepulverized coal in reduction areas RA becomes shorter, and then the NOxconcentration in the combustion gas can not be lowered.

As compared with the burner of FIG. 1, a burner 1 of FIG. 9, which isanother embodiment, further comprises a swirl-producing device 53 forswirling the mixture 12, and flow-rectifying plates 54. Hereinafter, theparts which are identical in construction or correspond in effect tothose of the above embodiment will be designated by the same referencenumerals, respectively, and explanation thereof will be omitted.

The swirl-producing device 53 is placed upstream of the guide 51.Accordingly, a larger amount of pulverized coal in the mixture flowsalong the inner peripheral surface of the flared distal end portion 14,thereby enabling the flame 5 to be further spread. However, if themixture is supplied in the form of a swirling flow into a furnace 3,such mixture is immediately mixed with the secondary air or the tertiaryair in the vicinity of the burner 1, so that the low NOx combustion isnot effected. Therefore, the plurality of flow-rectifying plates 54 areprovided on the inner peripheral surface of the flared distal endportion 14 disposed downstream of the swirl-producing device 53 (FIG.10). With this construction, a circumferential velocity component of themixture 12 is suppressed while a forward velocity component thereof isincreased, and then the mixture is mixed with the secondary air and thetertiary air at a location far from the burner 1. As a result, thereduction areas are increased, so that the low NOx combustion ispossible.

As compared with the embodiment of FIG. 9, a burner 1 of FIG. 11, whichis another embodiment, further comprises a Venturi tube 55 providedupstream of the swirl-producing device 53. A throat portion of theVenturi tube 55 once converges the pulverized coal in an air-fuelmixture toward a radially-central portion of the mixture nozzle 10, anddirects it toward the swirl-producing device 53. With this construction,the pulverized coal in the mixture can flow more efficiently along theinner peripheral surface of the flared distal end portion 14. Therefore,the generation of NOx can be more suppressed.

As compared with the embodiment of FIG. 11, a burner 1 of FIG. 12, whichis a further embodiment, has an annular spacer 25 instead of the annulardeflection guide tube 24, the spacer 25 being provided at a distal endof the gas supply nozzle 20. An inner peripheral surface of the spacer25 is so flared that its diameter increases progressively along the flowof mixture, and an outer peripheral surface of the spacer 25 is parallelto an axis of the mixture nozzle 10. An end of the inner peripheralsurface of the spacer 25 and an end of the outer peripheral surfacethereof are interconnected by an end wall disposed perpendicular to theaxis of the mixture nozzle 10. With this construction, the secondary air22 flows along the flared inner peripheral surface of the spacer 25, andis spread into a furnace 3 as in the above embodiment. The tertiary air23 flows along the outer peripheral surface of the spacer 25, and issupplied into the furnace 3 from a radially-outward position, andtherefore is mixed with the flame 5 with a delay at a position far fromthe burner 1. As a result, the reduction areas are formed in thevicinity of the burner 1, and the generation of NOx can be suppressed.

As compared with the embodiment of FIG. 1, a burner 1 of FIG. 13, whichis a further embodiment, includes the mixture nozzle 10 whose distal endportion is not flared. The venturi tube 55 having a throat portion isprovided inside the distal end portion of the mixture nozzle 10 inopposed to the guide 51. In this embodiment, the mixture 12 out from thethroat portion flows along a flared inner peripheral surface of theVenturi tube 55 by means of the guide 51, and is spread into the furnace3. If the guide 51 is disposed downstream of the throat portion of theVenturi tube as shown in the drawings, a larger amount of the pulverizedcoal flows along the inner peripheral surface of the Venturi tube 55,and can be supplied into the furnace 3 in an outwardly-spread manner.

As compared with the embodiment of FIG. 1, a burner 1 of FIG. 14, whichis a further embodiment, further comprises air injection nozzles 61.Four air injection nozzles 61 (though the number of nozzles is notsignificant) are circumferentially equiangulary spaced from each other(FIG. 15). As shown in FIGS. 15A to 15C, the number of the nozzles 61may be 1 to 3, or may be 5 or more. Further, as shown in FIG. 15D, theremay be used an arrangement in which injected air jets 62 are slightlydeviated from an axis of the mixture nozzle. Further, as shown in FIG.15A, the nozzles 61 may not be arranged equiangulary.

The air injection nozzles 61 are provided immediately downstream of theflame stabilizer 13, and disposed between the mixture nozzle 10 and thegas nozzle 20. The air injection nozzles 61 are interconnected by pipes,and communicate with an external air compressor means. The pre-warmedair 62 from the air compressor means is injected through the nozzle 61toward the mixture flow in a direction substantially perpendicular tothe axis of the mixture nozzle. As a result, as shown in FIGS. 16 and17, a stagnation point is formed in the flow of the mixture 12 due tothe injected air 62, and a relatively-negative pressure area NP isformed downstream of the injected air 62 with respect to the flow of themixture 12. High-temperature combustion gas is carried by the injectedair 62 into the negative pressure area NP, thereby promoting theignition of pulverized coal in the mixture. As a result, the combustionin reduction areas is promoted, and also the flame temperature rises inthe vicinity of the burner 1, thereby promoting the expansion of theflame.

The air injection nozzles 61 may be movable in the direction of the axisof the mixture nozzle so as to effect the optimum air injection inaccordance with combustion properties of the pulverized coal as solidfuel, a burner load, combusting conditions and so on. Further, an airinjection nozzle may be so arranged that it can swing in a planeperpendicular to the axis of the mixture nozzle. If the injectionnozzles 61 are directed slightly toward the upstream side of the mixture12, an ignition area can be increased. Accordingly, high-fuel ratio coaland coarse pulverized coal whose ignition properties are not good can beused as solid fuel.

A burner 1 shown in FIGS. 18 and 19 differs from the burner of FIG. 14in the positions of mounting of air injection nozzles. As shown in FIG.19, the air injection nozzles 61 are disposed immediately downstream ofthe flame stabilizer 13, and are provided on the annular deflectionguide tube 24 of the gas nozzle 20. Air 62 is injected from the airinjection nozzle 61 toward a flow of the mixture. In order to inject theair 62 in such a manner that it can pass through the secondary air andthe mixture, a greater energy is needed as compared with the burner ofFIG. 14. However, a larger amount of high-temperature combustion gas iscarried by the injected air 62 and flowed into the negative pressurearea NP. Therefore, this is suitable for burning high-fuel ratiopulverized coal (having a smaller amount of volatile components).

A burner 1, shown in FIG. 20, is a combination of the constructions ofFIGS. 11 and 14. The above-mentioned operations and effects can beenjoyed in a combined manner.

The present invention can be used as a combustion apparatus, for examplea coal-burning boiler.

What is claimed is:
 1. A combustion burner comprising:a mixture nozzlewhich extends toward an interior of a furnace, and defines a mixturepassage through which a mixture containing powdered solid fuel and gasfor transferring said solid fuel flows, said mixture nozzle having adistal end portion extending to a distal end of said mixture nozzle, thedistal end portion being flared so that an entire flow passage area ofsaid mixture passage in the distal end portion increases progressivelyto the distal end in a direction of flow of said mixture; a flamestabilizer provided at the distal end portion of said mixture nozzle; agas supply nozzle radially surrounding said mixture nozzle and definingbetween said gas supply nozzle and said mixture nozzle a gas passagethrough which combustion oxygen-containing gas flow toward said furnace;and a flow guide provided within said mixture nozzle at a positionupstream of said flared portion of said mixture nozzle with respect to aflow of said mixture so as to make said mixture flow radial outwardlyalong an inner peripheral surface of said flared portion of said mixturenozzle.
 2. A combustion burner according to claim 1, in which said flowguide is provided at a position corresponding to an interconnectingportion between the flared portion of said mixture nozzle and theremainder of said mixture nozzle with respect to the direction of flowof said mixture.
 3. A combustion burner according to claim 1, furthercomprising a swirl portion provided on said guide so as to swirl saidmixture, and a rectifier provided on an inner peripheral surface of saidflared portion of said mixture nozzle so as to rectify the swirledmixture.
 4. A combustion burner according to claim 1, in which said gassupply nozzle defines a secondary air passage between said gas supplynozzle and said mixture nozzle, and a tertiary air passage between saidgas supply nozzle and an opening formed in said furnace, and in whichsaid burner further comprises separation means for radially separatingthe flow of said mixture flowing from the distal end of said mixturenozzle into said furnace, from the flow of said combustionoxygen-containing gas flowing from said tertiary air passage into saidfurnace.
 5. A combustion burner according to claim 1, in which a distalend portion of said gas supply nozzle is flared, and an angle betweensaid flared distal end portion of said gas supply nozzle and an axis ofsaid gas supply nozzle is substantially equal to or larger than an anglebetween the flared distal end portion of said mixture nozzle and an axisof said mixture nozzle.